Clamping device for metal stretching and straightening machine



Nov. 17, 1970 A; HERTL 3,540,257

CLAMPING DEVICE FOR METAL STRETCHING AND STRAIGHTENING MACHINE Filed Aug. 20, 1968 3 Sheets-Sheet 1 Fig 1 7 Au +|Ib Fig.2Cl A an 4 11b 9 1o 8 3s 5 4 i I. O 3g 7/ 77 w w Inventor ALBERT H ERT Nov. 17, 1970 A. HERTL 3,540,257

CLAMPING DEVICE FOR METAL STRETCHING AND STRAIGHTENING MACIHNIJ.

Filed Aug. 20, 1968 3 Sheets-Sheet 2 Fig. 1b 7 F j Q LXR 1! 1 Fig. 2b 0 Fig.3b' 1 M 1 Flghb' Inventor A as e: m n e an.

nrrmEA/EVJ Nov. 17, 1970 A ERTL T 3,540,257

CLAMPING DEVICE FOR METAL STRETCHING AND STRAIGHTENING MACHINE Filed Aug. 20, 1968 3 Sheets-Sheet 15 Inventor A L13 ER T HER 19 rr k MEYS United States Patent 3,540,257 CLAMPING DEVICE FOR METAL STRETCHING AND STRAIGHTENING MACHINE Albert Hertl, Duisburg, Germany, assignor to Hydraulik GmbH, Duisburg, Germany Filed Aug. 20, 1968, Ser. No. 753,965 Claims priority, application Germany, Sept. 8, 1967, H 63,829 Int. Cl. B2111 11/02 US. Cl. 72-302 6 Claims ABSTRACT OF THE DISCLOSURE An apparatus for chucking uneven plates or sheets and for subsequently stretching and straightening these sheets includes a drawing head which is movable toward and away from a stretching direction. The drawing head is connected for movement along with a traverse which carries a plurality of individual clamping jaw assemblies which are to be chucked or engaged with the sheet to be stretched. The clamping jaw assemblies include a cross piece which is centrally pivotally supported by a push rod member which, in turn, is actuated by a fluid motor for movement toward and away from the plate to be chucked. In the initial position of operation the cross piece bears with its flat end against the end of the traverse so that it cannot pivot about its connection with the push rod of the fluid motor so that it must move in a parallel direction when the traverse is moved. The traverse is movable toward or away from the drawing head portion which carries space wedge members which are arranged on opposite sides of the sheet to be clamped. In addition, the traverse may move along with the drawing head for combined movement of all of the clamping jaws with the drawing head.

The construction permits initial engagement of an uneven sheet when the traverse is moved toward the drawing head to cause the clamping jaws carried at the end of push rods which are pivotally connected to the cross piece to move downwardly on wedge members and engage the sheet from respective opposite sides at aligned locations. After this initial engagement in accordance with the method of the invention the fluid drive motor for the cross piece is actuated which causes an initial backward movement of the transverse relative to the drawing head so that the cross piece may tilt relative to the traverse and thus permit those jaws which have not fully engaged the sheet to move by a necessary amount in order to effect proper engagement.

SUMMARY OF THE INVENTION This invention relates in general to a method and apparatus for chucking uneven plates or sheets which are to be stretched, and in particular to a new and useful device which permits shifting of individual jaws which engage from opposite sides of the sheet member after initial engagement of one of the jaws of each set with the sheet member whereby to permit the proper engagement of the jaws to the sheet member in the event that the sheet member is uneven, and to a method of chucking uneven plates or sheets of irregular thickness.

Metal sheets which are to be stretched are chucked or clamped by means of a plurality of clamping engagement or clamping jaw sets which are distributed across the width of the sheet and which are carried on a traverse which is movable toward and away from the stretching direction. The clamping elements include pairs of clamping jaws which are carried on a cross head which is articulated by a fluid pressure operated motor carried by the traverse. The drawing head includes wedge elements 3,540,257 Patented Nov. 17, 1970 "ice which act on the jaws to close them against the plate and during stretching the jaws act similar to the selfclosing jaws of a tensile testing machine. Plates or sheets which are absolutely straight and are of constant thickness at the location of the clamping elements can be gripped tightly without any difficulties with all of the well known chucking apparatus. However, since the plates or sheets do not have straight or even clamping ends but nevertheless must be gripped tightly over their entire width, a special design of chucking device and extra accessories are necessary. The thickness differences which are prevalent are usually of the order of several tenths of a millimeter to a few millimeters at most. Curvatures of the sheet ends and inclination effected by a skew form of the sheets may result in deviations from the horizontal by several centimeters.

In order to press sheet ends fiat, the feet of the individual pairs of jaws have usually been equipped with great driving power. By using sufficient power, the flattening of the sheet ends can be accomplished, for exam ple, in the manner of the straightening of a girder on two supports. This results in the centering of the sheet in the vertical direction in respect to the drawing head and, finally, because of the separate drive of each pair of jaws, the gripping of all pairs of jaws is accomplished. For thick sheets and particularly when a sheet end is wavy such as when the distance of the supports of the comparable girder on two supports is very short, it can be readily seen that the required power for flattening will soon assume values which would require an intolerable expenditure. Otherwise, the pair of jaws will not close at the respective point and only one jaw of the pair will make the contact with the sheet. Even during the subsequent stretching the equipment will not effect the closing of the pair of jaws since it would no longer be capable of doing this because of the tight closing of other more advanced pairs of jaws. Thus, the sheet would not and could not be gripped at all these points.

In accordance with the invention, a chucking method for curved or oblique sheets of irregular thickness is provided which insures that all pairs of jaws grip the sheet gradually in successive steps at all points over the entire width before the stretching process is started. This is achieved by advancing each pair of jaws jointly in the manner of continuous undivided pair of gripping bars and using relatively low driving power until the jaws come in contact with the sheet and up to the start of the position at which the flattening of the sheet takes place. In this manner, a clamping action or adhesive connection is first established between the clamping device and the sheet. The pairs of clamping jaws are then moved jointly and rigidly because the jaw linkages bear rigidly on a chucking traverse. Then the drawing heads of the stretching and straightening machine are moved in a stretching direction. While the jaw drive is maintained, the wedge surfaces of the drawing head are moved relative to the wedge-shaped jaws so that they are moved inwardly and effect a flattening of the sheet end with any required power, since the stretching drive acts to provide jaw feeding power.

When the flattening process is completed, which can be recognized by the increase of stretching power which is required, the movement of the drawing head is stopped. With the drawing head standing still, those jaws of the pairs of clamping jaws are advanced by the drive mechanism in a manner permitting engagement of the individual jaw elements which could not be gripped because of thickness differences at a previous time. After this occurs and all of the jaw elements of the pairs of jaws have gripped all points of the sheet widths without regard to thickness variations, the stretch straightening process can be effected with all clamping jaws closed.

In accordance with the invention, an apparatus for effecting the method includes a traverse which is movable relative to a drawing head and which carries a fluid motor for shifting a cross piece which is pivotally centrally connected to a piston rod member of the driving motor. The drawing head includes wedge-like elements which are arranged on each side of the sheet and which may be moved relative to wedge-shaped jaws carried at the ends of push rods which are pivoted at their inner ends to the cross piece. The drawing head may be moved relative to the traverse to cause the jaws to move along the wedge surfaces of the wedges carried by the drawing head and engage against the plates to be stretched. In addition, the traverse may be moved relative to the drawing head away from the cross piece after initial engagement to permit the tilting of the cross piece and the movement of one jaw relative to the other jaw to cause a firm flattening and engagement of the plate as required. Thereafter, the drawing head with the traverse may be moved in a stretching direction to carry out the stretching action. The traverse carries a plurality of individual clamping jaws assemblies which may be distributed across the width of one end of the sheet to locate the individual jaws in association with the wedge members of the drawing head. The drive for the cross piece which permits separate movement of the individual jaws on opposite sides of the sheet is advantageously of an elastic nature such as a fluid drive, for example.

Accordingly, it is an object of the invention to provide a metal sheet stretching device including a drawing head which may be moved toward and away from the stretching direction and which carries a traverse which is either movable therewith or movable relativethereto, and wherein individual clamping jaw elements which are adapted to be arranged at respective opposite sides of the sheet may be moved by the motor drive to cause initial engagement thereof at aligned opposite sides of the sheet and thereafter movement of the jaws individually to cause a firm gripping engagement by each jaw and the flattening of the sheet prior to the movement of the whole assembly in a stretching direction.

A further object of the invention is to provide a method of chucking an uneven metal sheet for stretching purposes which includes moving the chucking jaws to a position to initially engage the sheet from opposite aligned sides of the sheet and thereafter driving the jaws to permit shifting andflattening engagement of each jaw separately with the sheet, and thereafter moving the gripping jaws and the drawing head in a sheet stretching direction.

A further object of the invention is to provide a chucking device, particularly for chucking uneven metal plates, which is simple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there are illustrated and described preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1a is a partly schematic side elevational view of a drawing head and clamping jaw mechanism of a sheet stretching machine constructed in accordance with the invention;

FIG. 1b is a section taken along the line 1b--1b of FIG. la;

FIG. 2a is a view similar to FIG. 1a but showing the parts in a position at which they initially engage the sheet;

FIG. 2b is a section taken along the line 2b-2b of FIG. 2a;

FIGS. 1b and 2b are enlarged views corresponding to FIGS. 1b and 2b;

FIG. 3a is a view corresponding to FIG. 1a but indicating the parts in a position of a further gripping of the plate;

FIG. 3b is a sectional view taken along the line 3b--3b of FIG. 3a;

FIG. 4a is a view corresponding to FIG. 1 but indicating the parts in a final gripped position during the stretching operation;

FIG. 4b is a sectional view taken along the line 4b4b of FIG. 4a; and

FIGS. 3b and 4b are enlarged views corresponding to FIGS. 3b and 4b.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings in particular, the invention embodied therein as indicated in FIG. 1a comprises a stretching and straightening machine which includes two drawing head assemblies generally designated 30 (only one of which is indicated) which are arranged at respective opposite ends of a sheet of metal material to be straightened and stretched.

In accordance with the invention, the drawing head assembly 30 includes a drawing head member 4 which is movable toward and away from a stretching direction and which carries a pair of wedge elements 3 and 3' which may be oriented in respect to the end of a sheet of metal 11 which is to be stretched and straightened. The drawing head 4 is mounted on a member, for example, of a type indicated at 32, to permit its displacement in respect to the associated sheet 11 and the member 32 also carries a slide or support member 34 which may move with the drawing head 4 or relatively thereto. The member 34 carries a chucking traverse 7 which supports a driving motor such as a fluid pressure operated piston and cylinder drive generally designated 9.

The fluid pressure piston cylinder drive 9 includes a cylinder 36 secured to one end of the traverse 7 in which is slidable a piston 9 having a piston rod 8 which is pivoted centrally to a cross piece 6. The cross piece 6 is located on the opposite side of the traverse 7 and has a straight edge 6' which bears against a corresponding straight edge 7' of the traverse. In the position indicated in FIG. 1a this straight edge 7' orients the cross head 6 in a vertical plane. A spring 10 located within the cylinder 36 biases the piston 9 to the left to hold the cross head 6 against the end of the traverse 7, as shown.

Generally, a plurality of traverses 7 are provided across the width of the sheet 11 and each carries clamping jaw elements 1 and 1' which are pivoted to outer ends of push rods 5 and 5, respectively. The push rods 5 and 5' are pivoted at their inner ends at pivot points 38 and 40 at equally spaced locations from a central pivot 42 for the cross piece 6. When the cross piece 6 is held in the vertical position by the traverse 7, as shown, the push rods 5 and 5 will hold the jaws 1 and 1 such that their wedge-shaped surfaces 44, 44 bear against the complementary surfaces of wedge members 3 and 3' of the drawing head 4 at aligned locations. The traverse 7 extends over the width of the sheet and can be moved in the drawing head 4 on a parallel guide such as the guide 32 by means of an elastic drive such as a fluid pressure drive (not shown) toward and away from the plate 11 in either a non-stretching or a stretching direction.

When the fluid pressure cylinder 36 is admitted with a pressure such as a hydraulic or pneumatic pressure, the spring 10 is compressed and the cross piece 6 may move away from the edge 7' of the traverse 7. The push rods 5 and 5' and their associated jaws 1 and 1' are thus individually advanced so that all of the jaws may make contact with the sheet 11 to be stretched. Since the piston 9 is displaced by fluid pressure, when the clamping jaws 1 and 1' actually engage the sheet 11 during the stretching process, all jaws are supported elastically and individually in both directions of movement so that in case a sheet 11 breaks, the anticipated forces acting on the push rods 5 and 5' will be elastically absorbed.

In FIGS. 1a and lb, the starting position for chucking and stretching a sheet 11 is indicated. The sheet 11 is introduced into the drawing head 4 but the clamping jaws 2 have not yet been actuated.

In FIGS. 2m and 2b, the first chucking step is carried out wherein the traverse 7 has been moved by a power drive (not shown) in the direction of the sheet 11 and all pairs of jaws which extend across the sheet 11, and are generally designated by the numeral 2, move jointly. Because the cross piece 6 bears against the surface 7', each jaw 1 and 1' is displaced by the same amount since the cross piece may not tilt. As can be seen from FIG. 2b, the individual jaws I touch the sheet 11 partly at the top of the location 0 and partly at the bottom of the location u. An adhesive joint between the sheet and the clamping device 2 is thus formed. The sheet 11 is only straightened to the extent that it is possible as determined by the width of the jaw elements and since the top jaw 1 and the bottom jaw 1 mOVe by the same distance, one or the other of them may not be in contact with the sheet 11.

During the subsequent movement of the drawing heads 4 in a stretching direction, that is away from the sheet 11, the wedge members 3 and 3' move over the jaws 1 and 1 and compress them against the sheet similar to the action of a self-tightening jaw of a tensile testing machine. This action enforces the flattening of the sheet end. This state is represented by the position of the parts indicated in FIGS. 3a and 3b. It should be noted that the jaws 1 and 1' have still been moved in synchronism since the cross piece 6 still remains against the traverse 7. The thickness differences of the sheet 11 are therefore still not equalized. At this stage of the method of the invention the fluid pressure cylinders 36 are ad mitted with fluid pressure to displace the piston 9' against the force of the spring 10. However, because the jaws 1 and 1 have already gripped the metal plate 11 very tightly, the chucking traverse 7 must move backwardly in a direction toward its drive (not shown) and this releases the cross piece 6 from the traverse 7, as indicated in FIGS. 4a and 4b. The cross piece 6 may therefore pivot about the pivot 42 and the individual jaws 1 and 1' may move individually to make full contact with the sheet 11 as necessary. It may happen that the jaws 1 and 1 will advance by a dififerent amount as indicated in FIG. 4 if this is caused by the cross sectional form of the sheet 11. After the position of FIGS. 4a and 4b have been reached, the stretching process is carried out by the full gripping of all of the pairs of jaws 2 and the movement of the drawing head 4 in a stretching direction.

The showings in FIGS. 1b, 2b, 3b and 4b are similar to those of 1b, 2b, 3b and 4b but indicate more clearly the manner in which the jaws 1 and 1' grip the plate 11.

What is claimed is:

1. A clamping device for a metal stretching and straightening machine comprising a drawing head having a pair of wedge-shaped surfaces adapted to be positioned on respective opposite sides of a metal plate workpiece, a traverse located adjacent said drawing head, means mounting said drawing head and said traverse for combined movement and for relative movement toward and away from the workpiece, first and second clamping jaws located for positioning on respective opposite sides of the workpiece and having complementary wedge-shaped surfaces engageable with the wedge-shaped surfaces of the drawing head, the wedge-shaped surfaces being such as to cause inward relative movement of the jaws in respect to each other to engage the workpiece from respective opposite sides when the jaws are moved toward said drawing head wedge-shaped surfaces in a direction opposite to the stretching direction of the workpiece, a fluid-pressure drive carried by said traverse, drive means connected between said pressure drive and said first and second clamping jaws effecting shifting of said first and second clamping jaws by equal amounts to engage the jaws with the workpiece from aligned locations at respective opposite sides, said drawing head with said wedge-shaped surfaces being movable relative to said traverse and said first and second clamping jaws to cause an initial engagement of said clamping jaws with the workpiece, said drive means permitting relative displacement of said traverse relative to said first and second clamping jaws and the individual movement of said clamping jaws in a direction toward the workpiece by an amount sufficient to cause each of the jaws to tightly engage the workpiece, said traverse and said drawing head being movable away from said workpiece in a stretching direction for stretching the work piece.

2. A clamping device according to claim 1, wherein said drive means comprises a cross head, said fluid pressure drive including a piston rod pivotally connected to said cross head intermediate its width, said cross head having a fiat surface which is engaged with the surface of said traverse to maintain said cross head in a fixed position when said first and second clamping jaws are initially driven into clamping position, said drive means further including a first push rod connected to said first clamping jaw and a second push rod connected between said cross head and said second clamping jaw, said cross head being movable relatively away from said traverse after initial clamping engagement of said first and second clamping jaws with the workpiece and being pivotal about its connection with the piston rod to permit a further advance of one clamping jaw in respect to the workpiece than the other as necessary to effect a firm gripping of each of the clamping jaws with said workpiece.

3. A clamping device according to claim 1, wherein said traverse extends across the width of the sheet, said fluid pressure drive comprising a fluid pressure cylinder secured to one end of said traverse, a piston slidable in said cylinder and having a piston rod extending to the opposite end of said traverse, said drive means including a cross head pivotally connected at its center to said piston rod, said cross head having a fiat surface engaged with the fiat surface of said traverse and holding said cross head in a fixed position, said drive means further including a push rod pivotally connected to said cross head and to said first clamping jaw and a second push rod pivotally connected to said cross head and to said second clamping jaw, said cross head being pivotal to permit a further advance of one of said clamping jaws relative to the other when said cross head is moved away from said traverse.

4. A clamping device for a stretching machine comprising a cross piece, a drive member movable toward and away from the workpiece and pivotally connected centrally to said cross piece, first and second clamping jaws adapted to be positioned on respective opposite sides of the workpiece, a first push rod pivotally connected to said cross piece adjacent one end thereof and pivotally connected to said first clamping jaw, a second push rod pivotally connected to said cross piece adjacent the opposite end and pivotally connected to said second clamping jaw, Wedge means adjacent said first and second clamping jaws for directing said clamping jaws inwardly to engage a workpiece when said jaws are moved toward the Workpiece, and means for holding the cross piece in a fixed position during movement of said member for moving said first and second clamping jaws by the same amount and for permitting the pivoting of said cross piece relative to said member to permit a further movement of one of said clamping jaws and relative to the other of said clamping jaws to permit each of said clamping jaws to uniformly engage the workpiece.

5. A method of clamping a workpiece to be straightened and stretched using first and second clamping jaw members which are adapted to engage the workpiece from opposite sides and wedging means for Wedging the members inwardly toward the workpiece when the jaws are moved in a direction toward the workpiece, and also using a drive for advancing the clamping jaws toward the wedges, comprising the steps of moving said clamping jaws by equal amounts to engage the workpiece at respective opposite sides of the workpiece and at aligned locations, thereafter moving the wedging means in respect to the clamping jaws to tightly engage the clamping jaws with the workpiece, thereafter permitting independent movement of said clamping jaws relative to the workpiece in order to cause any jaw which has not firmly engaged the workpiece to move an additional amount to engage therewith.

6. A method according to claim 4, wherein the clamping jaws are moved jointly and rigidly by power-driven chucking traverse until it comes in contact with the work piece and until the flattening of the sheet takes place while the drive of the clamping jaws is maintained and the wedging means are directed toward the clamping jaws to cause the flattening of the workpiece and the engagement of the jaws with the workpiece, stopping the drawing head movement after the flattening is completed and then driving the jaws by a separate drive of each clamping jaw to permit individual gripping of each clamping jaw with the workpiece, and thereafter directing all of the clamping jaws and the drawing head in a direction to cause stretching of the sheet.

References Cited UNITED STATES PATENTS 3,082,809 3/1963 Petsch et al 72302 FOREIGN PATENTS 1,144,220 2/1963 Germany.

CHARLES W. LANHAM, Primary Examiner M. J. KEENAN, Assistant Examiner US. Cl. X.R. 

